This study aims to assess the validity of preventive pelvic floor exercise (PFE) for pregnancy-related stress urinary incontinence (SUI) and for the restoration of postpartum pelvic floor muscle strength. PFE is an accepted component of antenatal care. It is a non-invasive, non-pharmacological nursing intervention that has the potential to lessen perineal trauma resulting from pregnancy and childbirth. A well-exercised pelvic floor musculature may more effectively support the proximal urethra, more readily accommodate the passage of the infant, and more rapidly regain function in the postpartum. Preliminary work has shown that postpartum pelvic muscle strength is related to the incidence of SUI. However, currently there is no clear empirical evidence to support the contribution of PFE to postpartum pelvic muscle strength or the incidence of SUI. This is a randomized clinical trial of postpartum pelvic floor outcomes using one intervention and one non-treatment control group; outcomes will be evaluated by a clinician blind to group assignment. Three hundred primigravid and secundagravid women will be recruited. Baseline data on pelvic floor muscle status and SUI signs and symptoms will be collected at 20 weeks gestation. Repeated measures will be obtained at 35 weeks gestation and at 6 weeks, 5 months, and 12 months postpartum. Relationships between antepartal PFE and postpartum pelvic muscle strength and the incidence of SUI will be tested. Thus, this study will strengthen the research base for the nursing practice of teaching PFE and contribute to the scientific literature about health promotion and disease prevention. Nursing has a long tradition of using physical procedures as an opportunity for client education. A vaginal examination provides an excellent experience in which a woman can learn about proper PFE technique and the benefits of this practice. Nurses also monitor postpartum perineal status and counsel women about self-care practices. Thus, this area is especially salient to nurses because they are ideally situated to disseminate knowledge about the contribution of PFE to the health of childbearing women.